Shoulder/unit turn, more than 90 degrees?

I have the habit of turning my shoulder on groundstrokes just about 90 degrees so I just look over the shoulder whenever I set up for the forehand and backhand. However, recently I have been thinking that even a 90 degree turn doesn't give me enough consistency and power, and my laid-back wrist doesn't seem to stay the way I want it to, and as a result I often find myself lunging at the ball instead of meeting it square on in the middle of rotation.

Then I looked at some vids of pros practicing, such as Fed and Nadal. It seems that for them, even for semi-open stance forehands, the shoulder is turned more than 90 degrees when setting up a forehand. This turn is even more pronounced when they are hitting their backhands as it requires an even more closed stance. Often times they are facing the court with half their back instead of having their shoulders parallel to the sidelines. This seems to conserve more energy and delays the point of contact in the kinetic chain to even later so they are not lunging at the ball.

So what I am asking is, is it normal to turn the shoulders more than 90 degrees when setting up for a groundstroke? This may sound like a fussy question but I will jump on any opportunity to improve my game.

Do what feels natural. As long as you don't rotate your trunk (your legs, etc) more than 90 degrees and it's just your upper body going a little bit more, it should be fine. Once you do closed stance and turn past 90 degrees with your legs, you lose a ton of power potential and should try to avoid this if at all possible on any shot other than the slice or if you have a 1HBH, which allow for more closed stances.

In Elliott's book he discusses on the forehand that the shoulders should turn back farther than the hips so that some trunk muscles get pre-stretched for the swing (search: stretch-shortening cycle). He discusses the desirable angle range for the difference between the shoulders and hips - for an effective twist of the trunk.